Three groups of experiments are proposed to (1) characterize the human neonate's adrenocortical and behavioral responses to stressors and their interrelationships, (2) examine the effects of soothing practices on behavioral and hormonal responses to stressors, and (3) examine individual differences in biobehavioral stress responses and their antecedents during the neonatal period. Male neonates will serve as subjects, the majority being between 3 and 5 days of age. In most experiments the stressor will be neonatal circumcision and the events surrounding circumcision. Activity of the pituitary-adrenocortical system will be examined using measures of serum cortisol. Serum samples will be obtained from scalp veins. Behavioral observations using a 30-sec coding interval will be used to obtain measures of behavioral state. In addition, the Brazelton Neonatal Behavioral Assessment Scale will be used to examine the organization of the neonate's behavior and reactivity to stimulation before and after circumcision. The proposed experiments will provide basic data in the area of psychobiology as such information pertains to child development and pediatric behavioral medicine. The long-term goals are to gain a better understanding of stress and coping in the human infant.